Center electrode structure for spark plugs and process for making the same



Qct. 4, 1950 o. BEESCH 2,955,222

CENTER ELECTRODE STRUCTURE FOR SPARK PLUGS v AND PROCESS FOR MAKING THESAME Filed June 24, 1959 FIG. 1

mwggfl II MEN- its? 2,955,222 Patented Get. 4, 1960 ice CENTER ELECTRODESTRUCTURE FOR SPARK PLUGS AND PROCESS FOR MAKING THE SAME Otto Boesch,Stuttgart-Zulfenhausen, Germany, assignor to Robert Bosch G.m.b.H.,Stuttgart, Germany Filed June 24, 1959, Ser. No. 822,596 Claimspriority, application Germany June 25, 1958 Claims. (Cl. 313-141) Thepresent invention relates to spark plugs.

More particularly, the present invention relates to that part of a sparkplug which forms the lower end section of a center electrode of thespark plug.

It has already been proposed to extrude a pair of blocks of differentmetals into such a lower end section of a center electrode in such a waythat one of the blocks forms an envelope in which a shank formed fromthe other block is embedded. However, considerable difiiculty andexpense is involved in joining to such a structure the sparking pointwhich is made of a metal such as platinum, osmium or tungsten.

One object of the present invention is to provide a special billet withwhich a sparking point assembled in such a way as to be properlyconnected to the remainder of the structure as a result of the extrusionso that it becomes unnecessary to assemble such a sparking point withthe lower end section of the center electrode after extrusion of thislower end section.

It is also an object of the present invention to provide a processaccording to which a billet is extruded into the lower end section of acenter electrode of a spark plug in such a way that a sparking point ispermanently connected with this section of the center electrode.

It is also an object of the invention to extrude a structure whichrequires practically no further working before it is assembled into thespark plug.

With the above objects in view, the present invention includes a centerelectrode structure of a spark plug, this center electrode structureincluding an outer envelope of one metal in which a shank of a coremember of a different metal is embedded. A sparking point extends inpart into an end wall of the envelope, and the material of this end wallpresses against and surrounds the sparking point to fix the latter tothe envelope. The assembly of the above elements, namely, the outerenvelope, the core member and the sparking point, is extruded in onestep according to the present invention, from a billet made up of a pairof blocks of different metals located closely adjacent to each other andadapted to be extruded into a structure wherein one of, the blocks formsthe above envelope and the other of the blocks forms the above coremember whose shank is embedded in the envelope and, in accordance withthe present invention, that block of the billet which subsequently formsthe envelope has fixedly connected thereto, before the extrusion takesplace a sparking point which is positioned in such a way that at the endof the extrusion, part of the sparking point is embeddedin an end wallof the envelope.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims- Theinvention itself, however, both as to its construction and its methodof'operation, together with additional objects and advantages thereof,will be best understood from the following description top end portionsurrounding the lower portion of the head'- of specific embodiments whenread in connection with the accompanying drawings, in which:

Fig. 1 is a fragmentary sectional diagrammatic view of an extruding dieand ram used to extrude the billet structure illustrated in Fig. 1 intothe structure illustrated in Fig. 2; V

Fig. 2 is a partly sectional elevational view of an unfinished lower endsection ofa center electrode of a spark plug, this lower end sectionbeing extruded from the structure illustrated in Fig. 1;

Fig. 3 shows the finished lower end section of the center electrodewhich is formed from the structure of Fig. 2;

Fig. 4 is a top plan view of the structure of Fig. 3;

Fig. 5 is a fragmentary sectional illustration of another embodiment ofan extruding die and ram and billet assembly extruded thereby; and

Fig. 6 shows the structure resulting from the extrusion of the billet ofFig. 5 with the press of Fig. 5.

Referring now to Fig. 1, the structure illustrated therein includes thedie 1 formed with a receiving chamber 2 for receiving the billetassembly illustrated in Fig. 1. The chamber 2 communicates with thedischarge opening 3 of the die 1, this discharge opening 3 communicatingin turn with a bore portion 4 of an enlarged diameter as compared to thedischarge opening 3. The chamber 2 is joined to the opening 3 by afrustoconical bore portion 5 whose angle of inclination 0: isapproximately 30 in the illustrated example.

The billet assembly of Fig. 1 includes a sparking point 6 made of anoble metal such as platinum. It will be noted that the sparking point 6has an enlarged frustoconical head and is received in an opening of thelower block 7 of the illustrated billet assembly. This opening extendsthrough the block 7 and has an enlarged frustoconical configurationadjacent the upper face of the block 7 to receive the enlarged head ofthe point 6. The point 6 has an inner shank portion pressed into theopening of the block 7 and an outer shank portion extending freelybeyond the block 7 before extrusion takes place, as illustrated inFig. 1. The block 7' may be made of nickel and after the point 6 isassembled therewith, a layer of silver solder 8 is located between andfused with the blocks 7 and 9 to form the billet assembly illustrated inFig. 1. The upper block 9 of Fig. 1 maybe made of copper, and theillustrated billet assembly is inserted as a unit into the receivingchamber 2'of the die 1.

With the above-described billet thus located in the die 1, the ram 11-of the extrusion press, which is provided with the conical end face 10,is axially pressed into the chamber 2 so as to extr-ude the billetthrough the bore portion 5 and the discharge opening 3' until thestructure has the configuration illustrated in- Fig. 2. When the billetof Fig. 1 has been extruded into the structure shown in Fig. 2, theextrusion is stopped, the ram 11 is retracted, and the extruded articleis removed from the die in an-upward direction, as viewed in Fig. 1,opposite to the direction of movement of the ram 11 during extrusion, sothat in this way the extruded article of Fig. 2 is separated from thedie 1.

As is shown at the right, sectional portion of Fig. 2, the platinumsparking point 6 has'been changed only to a slight degree, while theblock 7 has been formed into the envelope 7 in which the elongated shankof the coremember 9 is embedded. The core member 9 has an enlarged headend, and the envelope 7 has an enlarged end of the core member 9 whichis located next to the shank thereof. As a result of this construction,the envelope 7 extends upwardly beyond the shank of the core member 9 sothat it is the upper part of the. envelope 7 which rests on a matingshoulder of the electrical nonconductive insulating body of the sparkplug when the structure of Fig. 2 is assembled therewith. Thisconstruction is of considerable advantage in that the corrosion actionof the combustion gases can extend during operation only along the shankup to the enlarged head of the core member, so that the envelopeprotects the entire core member in this way against such corrosion.

' The structure of Fig. 2 may be finished to form the structure shown inFig. 3. Since the upper part 12 of the structure of Fig. 2 is composedof copper, it is easy to work. Thus, this upper part 12 may be placedbetween three jaws similar to the jaws of a chuck and these jaws aresimultaneously moved toward each other along radial lines extending fromthe center of 'a circle along which the jaws are located so that bypressing the upper part of the assembly in this way, it is formed intothe connecting portion 13 shown in Figs. 3 and 4, this electricalconnecting portion 13 being: made up of three fins'spaced from eachother by 120 as shown most clearly in Fig. 4. The excess material of thehead portion 12 illustrated in Fig. 2 is turned off to form the collar14 illustrated in Fig. 3. Also, at the lower end of the assembly in thevicinity of the sparkingpoint 6, the envelope 7 is turned oif asindicated at 15 in Fig. 3 so that when the structure of Fig. 3is'assembled with the rest of the spark plug structure, aheat-insulating air gap will be The noble metal which forms the sparkingpoint 6 or 6' neednot necessarily be platinum and can be, for example,alloys of osmium or tungsten. If it is desired to avoid the relativelyhigh pressure required by the ram 11', inasmuch as this ram does notinclude a forwardly projecting end similar to the end 10 of the ram 11which first engages the core-forming block only at a central portionthereof, it is possible to reverse the ram structure by providing thebottom end of the ram 11 with fins similar to the fins 13 so as to formin'the upper portion of the extruded structure a Y-shaped opening, sothat with this construction the electrical connecting member. is formedby a member having a Y-shaped opening'rather than fins. With such aconstruction, the ram need not be applied with as high a pressure as isrequired by the structure of Fig. 5.

The envelope 7 or 7 can be made of nickel, chromium or alloys thereof. 7

In the past, in order to save costs, a sparking point of a noble metalhas been joined to an element such as the envelope 7 as by being weldedthereto. However, because of the small dimensions of the parts, they aredifficult to handle and the manufacturing costs are relatively I high.Furthermore, the welding of a sparking point of formed around this lowerportion of the assembly of Fig. 3 between the latter and the outerceramic insulating body of the spark plug. The embodiment of theinvention which is illustrated in Fig. 5 shows several simplificationsas compared to the above-described structure, and these simplificationsresult in a substantial reduction in the manufacturing costs. Theplatinum sparking point 6' is considerably shorter than the sparkingpoint 6 and the opening of the nickel billet block 7 which receivespoint fi'extends only partly through the block 7'. The sparking point 6'is fixed to the billet block 7 by being Welded or soldered theretobefore the extrusion takes place. Also, the billet assembly of Fig. 5diifers from that of Fig. 1 in that the copper block 9. is directlywelded to the nickel block 7', and the billet assembly 6', 7' and 9 isinserted as a unit into the receiving chamber 2' of the die 1. Thefusing of the billet blocks 7 and 9' to each other can easily be carriedout in a protective gas atmosphere composed of a gas or gases which areinert with respect to the materials being fused to each other at thefusing temperature.

Also, it will be noted from a comparison of the die 1' of Fig. 5 withthe die 1 of Fig. 1 that the ratio of the diameter of the receivingchamber 2' to the discharge opening 3' is smaller than in the embodimentof Fig. l, and also, it will be seen that the extruding ram 11 is formedwith an opening 10 which has the configuration of the connecting portion13' illustrated in Fig. 6. This connecting portion 13' is substantiallyidentical with the connecting portion 13 of Fig. 3 so that with thestructure of Figs. 5 and 6, the Y-shaped connecting portion 13 is formedduring the extrusion and does not require an additional step andstructure. The frustoconical bore portion 5' of the die 1' has aninclination different from the bore portion 5 of Fig. 1 because of thediiferent relationship between sizes of the openings and components, ofthe billet assembly. The billet assembly of Fig. 5 will be extrudeddirectly into the article shown in Fig. 6 except that there will bealong the outer periphery of the collar 14 at the end of the latterdirected toward the extruding ram 11' a burr which is easily removed.Upon removal of this burr, the structure shown in Fig. 6 is provided andmay be assembled directly with the remaining structure of the sparkplug, so that practically no working beyond the extrusion itself isrequired with the embodiment of Fig. 5.

Of course, some of the simplifications of Fig. 5 can b incorporated intothe other embodiment, of the invention.

noble metal to the envelope results in the unavoidable disadvantage ofpoor head conductivity. With the abovedescribed process and billetstructure, the resulting structure shown in Figs. 24 and 6 overcomes allof the above disadvantages and the sparking point is joined to theassembly in an extremely simple and effective manner guaranteeing thatduring the cold extrusion of the billet assembly not only will the lowercenter electrode structure be formed but, in addition, the sparkingpoint will be simultaneously securely anchored to the assembly with thelower free end portion of the sparking point 6 or 6' exposed in themanner illustrated in Figs. 3 and 6.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofspark plugs differing from the types described above.

While the invention has been illustrated and described as embodied incenter electrodes of spark plugs, it is not intended to be limited tothe details shown, since various modifications and structural changesmay be made without departing in any way from the spirit of the presentinvention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by V gated metallic core memberhaving an elongated shank;

an elongated metallic tubular envelope of a metal different from saidcore member, said shank being embedded in said envelope and saidenvelope having an end wall located beyond a free end of said shank andformed with an opening which opens onto an end face of said envelopewhich is directed away from the free end of said shank; and a sparkingpoint of a noble metal having an inner shank portion located in saidopening and at least part of the material of said end wall surroundingand pressing against said inner shank portion of said sparking point forfixing the latter to said envelope, said sparking point having an outershank portion extended freely beyond said end wall of said envelope.

2. For use in a spark plug, in combination, an elongated metallic coremember having an elongated shank; an elongated metallic tubular envelopeof a metal different from said core member, said shank being embedded insaid envelope and said envelope having an end wall located beyond a freeend of said shank and formed with an opening which opens onto an endface of said envelope which is directed away from the free end of saidshank; and a sparking point of a noble metal having an inner shankportion located in said opening and at least part of the material ofsaid end wall surrounding and pressing against said inner shank portionof said sparking point for fixing the latter to said envelope, saidsparking point having an outer shank portion extended freely beyond saidend wall of said envelope, said opening of said end wall of saidenvelope extending only partly through said end wall.

3. For use in a spark plug, in combination, an elongated metallictubular envelope of a metal different from said core member, said shankbeing embedded in said envelope and said envelope having an end walllocated beyond a free end of said shank and formed with an opening whichopens onto an end face of said envelope which is directed away from thefree end of said shank; and a sparking point of a noble metal having aninner shank portion located in said opening and at leastpart of thematerial of said end wall surrounding and pressing against said innershank portion of said sparking point for fixing the latter to saidenvelope, said sparking point having an outer shank portion extendedfreely beyond said end wall of said envelope, said opening of said endwall of said envelope extending only partly through said end wall andsaid sparking point having an enlarged head end embedded in said endwall of said envelope.

4. For use in a spark plug, in combination, an elongated metallic coremember having an elongated shank; an elongated metallic tubular envelopeof a metal different from said core member, said shank being embedded insaid envelope and said envelope having an end wall located beyond a freeend of said shank and formed with an opening which opens onto an endface of said envelope which is directed away from the free end of saidshank; and a sparking point of a noble metal having an inner shankportion located in said opening and at least part of the material ofsaid end wall surrounding and pressing against said inner shank portionof said sparking point for fixing the latter to said envelope, saidsparking point having an outer shank portion extended freely beyond saidend wall of said envelope, said opening extending through said end wallof said envelope.

5. For use in a spark plug, in combination, an elongated metallic coremember having an elongated shank; an

elongated metallic tubular envelope of a metal difierent from said coremember, said shank being embedded in said envelope and said envelopehaving an end wall 1c!- cated beyond a free end of said shank and formedwith an opening which opens onto an end face of said envelope which isdirected away from the free end of said shank; and a sparking point of anoble metal having an inner shank portion located in said opening and atleast part of the material of said end wall surrounding and pressingagainst said inner shank portion of said sparking point for fixing thelatter to said envelope, said sparking point having an outer shankportion extended freely beyond said end wall of said envelope, saidopening extending through said end wall of said envelope and saidsparking point having a head end pressed between said free end of saidshank of said core member and said end wall of said envelope.

6. A billet adapted to be extruded into an elongated body which forms atleast part of a center electrode of a spark plug, said billet comprisingin combination, a pair of blocks of different metals, respectively,located closely adjacent to each other, said blocks being adapted to beextruded simultaneously into an elongated body wherein one of the blocksforms a tubular envelope and the other of the blocks forms a core atleast part of which is embedded in the envelope, said one block beingformed with an opening extending at least partly into said one blockfrom an end face thereof which is distant from and directed away fnomsaid other block; and a sparking point carried by said one block in saidopening thereof and having an elongated free end portion extendingbeyond said end face of said one block, so that said free end portion ofsaid sparking point will be exposed after said one block is extrudedinto said envelope.

7. A billet as recited in claim 6 and wherein said blocks are fixeddirectly to each other.

8. A billet as recited in claim 6 and wherein a layer of solder islocated between and united with said blocks.

9. A billet as recited in claim 6 and wherein said opening of said oneblock extends entirely through the latter and has an enlarged portion ata face of said one block which is opposed to said end face thereof anddirected toward said other block, said sparking point having an enlargedhead end located in said enlarged portion of said opening.

10. A billet as recited in claim '6 and wherein said opening extendsonly partly through said one block and said sparking point having a headend in said opening fixed to said one block.

References Cited in the file of this patent UNITED STATES PATENTS

